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LOS ANGELES — California took a pounding from a powerful storm that collapsed the roof of a trade school, made roads treacherous and forced residents from homes out of fear of mudslides from fire-stripped hillsides.

Interstate 15, the main route connecting Southern California and Las Vegas, was closed by heavy snow in a mountain pass east of Los Angeles. Interstate 5 north of Los Angeles was snarled by snow that forced the California Highway Patrol to shepherd motorists over another pass.

About 20,000 customers lost power across the state, utilities reported.

At its height Monday, the storm triggered hundreds of fender-bender traffic accidents on freeways, highways and surface streets across California, Washington and Nevada.

In Anaheim, students and teachers fled a trade school when the roof of a classroom collapsed during heavy rain Monday. Twelve students and two staff members were hospitalized with mostly minor injuries, and all but one were released by afternoon, said Lynn Porter, assistant superintendent of educational services.

About 150 students were at the center, which prepares high school students and adults for medical occupations, said spokeswoman Pat Hansmeyer. Only three of the students were minors, and they were not injured, she said.

'Minor mud issues'In Yorba Linda, where 100 homes were lost to a wildfire last month, hundreds of residences in the canyon areas were ordered evacuated Monday morning because of the threat of mudslides. But the threat eased later in the day.

"We're getting some minor mud issues coming down, but we haven't really had any very large mudslide issues," said Lt. Gregg Hayden of the Brea Police Department, which serves Yorba Linda.

The area was one of several placed under a flash-flood watch because hillsides and canyons had been stripped of vegetation by recent wildfires, increasing the chances of severe flooding and mudslides.

A section of the Pacific Coast Highway in the Sunset Beach area was closed in both directions by flooding.

3 deaths linked to stormAt least three deaths were linked to the storm. A California Highway Patrol officer directing traffic around an accident in Hacienda Heights, east of Los Angeles, was hit by an out-of-control car, said patrol Officer Terry Liu. One person was killed in the San Diego area when an armored truck slid off a wet highway and rolled down an embankment.

Authorities said the storm also contributed to the death Sunday of a 61-year-old man who was washed off a jetty by large waves in Crescent City.

Ski areas east of Los Angeles got a big coating of snow, but travel in the rugged mountain resort region nearly impossible in many areas. At Lake Tahoe, Heavenly Mountain Resort reported nearly 18 inches of snow by Monday, and Squaw Valley USA reported 22 inches of new snow.

The storm had moved into California from Oregon, where it delayed flights out of Portland on Sunday and broke the record low temperature for the day Monday when the airport reported 22 degrees.

Some highways in northwestern Oregon were closed over the weekend because of icy conditions, and Interstate 205 was briefly closed Monday after a tanker full of deicing chemicals turned over.

It also brought snow and freezing weather to Washington state, where Seattle-Tacoma International Airport hit a record low of 19 degrees early Monday.